The Replication of Viruses Viruses must infect cells in order to reproduce themselves. Much of what we know about viral replication comes from studies of bacteriophage viruses that infect bacteria. The common intestinal bacteria Escherichia coli can be infected by T-phage who go through a lytic cycle (transduction), or by Lambda phage who stay dormant once they enter a cell. This is called LYSOGENY. How T-Bacteriophage Infect Bacteria The first stage of T-phage infection is to the cell wall of a bacterium. The phage does this using its . The of the phage then contracts downward. The tail releases an penetrates the wall and which is injected into the bacterial cytoplasm. This stage of infection is called of the virus is left outside the cell. Figure 1 – The Lytic Cycle . The Figure 2: The Lytic Cycle Now the stage begins. Using building blocks found in the bacterial cytoplasm, numerous copies of the and many molecules are produced. In the next stage of the cycle (the these molecules will be used to form new bacteriophages. The cycle stage), ends with the release of the new virus particles by It is this rupture that gives the curve is plotted, an initial . cycle, its name. If a growth period is seen. This corresponds to the stage of infection which takes place the bacterium. A rapid increase follows due to the release of many new T-phage viruses. The of the growth curve results when all of the bacteria in a culture are infected. Summary 1:Bacteriophage finds a suitable host; 2:The viral DNA is ejected through the tube into the bacteria; 3:The viral DNA takes over the bacterial machinery to produce new protein and DNA for the virus; 4:The bacterial particles assemble in the bacterial cell; and 5:The bacterial cell lyses to perpetuate the cycle of the bacteriophage.